The term "lost circulation" (or lost returns) is normally used to refer to a situation where substantial amounts of whole drilling and/or completion fluids (e.g. cements) and not just filtrate are lost to a highly permeable, fractured, or cavernous formation during the drilling and/or completion of a well. When lost circulation occurs, the fluid losses can range from a slow seepage to a complete loss of the fluid column in the wellbore. As is readily recognized in the art, lost circulation can be very difficult to control and the expense involved is usually substantial.
When lost circulation occurs, various materials are routinely pumped down the wellbore and into the permeable flow passages (e.g: fractures) in the formation in an attempt to bridge across and form a fluid barrier in these passages. By forming a barrier across the passages, flow is blocked therethrough which, in turn, prevents further propagation of the tip of the passage into the formation. Once the flow passages in the formation have been effectively bridged and/or blocked, full circulation of the fluids in the wellbore can be reestablished.
Where lost circulation fluid losses are small, it is common in the art to treat the lost circulation zone with fibrous, flake, or granular materials which are commercially-available and which are designed to help plug the passages in the formation. Where the losses are large, it is common to treat the loss circulation zone with "gunk" squeezes, polymers, calcium silicate gels, cements, etc..
While each of the above-described, prior-art treatments have proved successful in controlling lost circulation problems in the particular applications for which they were designed, no one material or treatment has been found to work in every lost circulation situation. Accordingly, the search continues for new, low-cost lost circulation treatments and materials.